Invalid pointer dereference in C++

bad_ptr.cpp

/** A simple example of an invalid pointer dereference.
 *  
 *  a is not a valid pointer until initialized, so dereferencing it (here,
 *  setting it to 37) is bad news.
 *
 *  Note that C++ doesn't necessarily initialize pointers to NULL, so it is
 *  possible that this will "work" and not cause a segmentation fault. This
 *  could be really bad, trampling some other memory. We're lucky to get a
 *  segfault.
 */

int main()
{
  // a is declared but not initialized...
  int* a;

  // then dereferenced. Bad news.
  *a = 37;

  return 0;
}